It is known, from British Pat. No. 1,037,741, to prepare flat or tubular net-shaped structures consisting of longitudinally oriented interlaced synthetic polymers, by producing, with the help of suitable cutting devices, a series of spaced, parallel slots in either a flat or tubular, mono-oriented polymer film, so that the successive transversal expansion of the slitted film will produce the net-like structure.
Net-shaped structures of an analogous type, although consisting of filaments interlaced in a much more irregular and casual manner, may be obtained, furthermore, by disaggregation or by slitting of the mono-oriented polymeric films by different methods, such as, for instance, by sandblasting, brushing or rubbing.
In general, the products thus obtained are bulky and flexible, and are used for manufacturing ropes, cords and strings and textile materials of various kinds.
It is also known, from Spanish Pat. No. 460,292, to use structures of that kind, opened by transversal or cross-expansion, in manufactured products based on inorganic hydraulic binders, in order to obtain an improvement of their mechanical characteristics.
Given the chemical incompatibility of the synthetic polymers in general for the inorganic materials that form the hydraulic binders, the polymeric structures thus used hardly adhere to the matrix of the binder, wherefore the reinforcing action is not altogether effective.
In British Pat. No. 1,316,661, there is described a process aimed at improving the characteristics of the manufactured products made of hydraulic binders, by means of a reinforcement with synthetic polymeric fibers additioned with 20-80% of cements. In such a case the fibers are of the conventional type with a high count (greater than 50 denier), and are cut into 50-30 mm long staples.
Similar fibrous compositions, to be used as reinforcement of manufactured products from hydraulic binders, are also claimed in published Japanese patent application No. 74/48.721. The use of this kind of reinforcement causes problems in the production of the fibers with regard to the high percentage of additive present, and does not allow to obtain manufactured products from hydraulic binders that will have satisfactory characteristics. More particularly, the resistance to bending of the reinforced manufactured products is only slightly higher than that of the non-reinforced products.